Various types of injection devices are available for assisting with the injection of a medicament into a patient (human or animal), and which are configured to receive a standard, pre-filled glass or plastic syringe tipped with an injection needle. These devices may have a dose setting mechanism and a main drive spring for driving a plunger into the syringe so as to expel the medicament out through the needle. Injection devices may comprise a further spring for driving the needle out of the device housing and into the patient's skin, prior to activation of the main drive spring to expel the medicament.
In order to maintain sterility prior to use, and to avoid “sticking” injuries, the pre-filled syringe is supplied to the injection device assembler with a rubber or rubber and plastic cap, known as a “sheath” or “boot”, covering the needle. The sheath has an interior space for containing the needle, and a sealing end that abuts the adjacent end of the syringe body to seal that inner space. In some cases, the sheath may also comprise a solid piece into which the needle is pushed. Immediately prior to use, a user (e.g. healthcare professional or patient) must remove the sheath to uncover the needle. This is typically achieved using a sheath removal tool that is inserted by a user into the injecting end of the device. The tool comprises a set of sprung fingers that ride over and along the sheath as the tool is pushed into the device. The fingers then snap into the junction between the syringe end and the sheath. The user can then pull out the tool, bringing the cap with it.
Particularly in the case of expensive medicaments, it is extremely important to minimise the failure rate of assembled injection devices. Considering the sheath removal solution outlined in the previous paragraphs, it may be difficult to achieve exactly the right degree of flexibility in the fingers to ensure that they can ride over the sheath whilst still providing sufficient force to close over the junction at the rear of the sheath.
GB 2438593 (Cilag), US2006/0100588 A1 (Brunnberg et al), WO 2007/047200 A1 (Eli Lilly), US 2006/0270986 A1 (Hommann et al), WO 2006/063015 A2 (Washington Biotech Corp.) and US 2004/010234 A1 all describe devices for housing syringes and removing sheaths therefrom.